Supersonic centrifugal compressor

ABSTRACT

The fixed portion of the rotor casing defines with the disc extension or a rotary disc carrying radially extending blades an annular deceleration space leading into a diffuser whose fixed vanes define passages inclined to the radial direction.

United States Patent Friberg et al.

[ Nov. 13, 1973 SUPERSONIC CENTRIFUGAL COMPRESSOR Inventors: Jean-MarieEugene Friberg,

Bourg-La-Reine; Jean-Marie Merigoux, Palaiseau, both of France Assignee:Societe Alsacienne De Constructions Atomiques- De Telecommunications EtDElectronique Alcatel, Paris, France Filed: Dec. 18, 1972 Appl. No.:315,961

Related U.S. Application Data Continuation of Ser. No. 104,876, Jan. 8,1971,

abandoned.

Foreign Application Priority Data Jan. 14, 1970 Japan 45/7001293 U.S. Cl415/181, 4l5/2l1, 4l5/2l9 A [51] Int. Cl. F04d 21/00, F04d 29/44 [58]Field of Search 415/1 19, 219 A, 213, 415/181, 211, 204, 206, 207

[56] References Cited UNITED STATES PATENTS 3,369,737 2/1968 Switzer etal. 415/211 3,378,229 4/1968 Erwin 415/211 3,460,748 8/1969 Erwin415/211 Primary Examiner-J-lenry F. Raduazo AttorneyDonald E. Zinn etal.

[57] ABSTRACT The fixed portion of the rotor casing defines with thedisc extension or a rotary disc carrying radially extending blades anannular deceleration space leading into a diffuser whose fixed vanesdefine passages inclined to the radial direction.

8 Claims, 2 Drawing Figures PATENIEDNUVISIQH 3771.925

- INVENTORS JEAN-MARIE E%GENE FRIBERG JEAN-MARIE M RIGOUX BY u.;\rur WMM.

ATTORNEYS SUPERSONIC CENTRIFUGAL COMPRESSOR This is a Continuation, ofapplication Ser. No. 104,876, filed Jan. 8, 1971, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention concerns a supersonic centrifugal compressor providing a highcompression ratio and increased output.

2. Description of the Prior Art lt has long been known that a fairlyhigh compression ratio may be obtained in a centrifugal compressor bygiving to the fluid under compression a high rotational speed and thentransforming the thus obtained kinetic energy into pressure.

It has already been proposed to transform this kinetic energy intopressure, very simply, by using a rotating diffuser whose profile isobtained by extending the radii of the rotating blade support discbeyond the blades. The expansion of the fluid between two walls bothmoving at speeds close to that of the fluid then takes place with afairly high efficiency.

Such devices, however, cannot be used when a high compression ratio,about 5 for example, is required with a single compressor stage. Forthis, the peripheral speed of rotation of the rotor blades must be ashigh as 400 or 500 meters per second, requiring even higher speeds atthe periphery of the rotating diffuser. Centrifugal stresses then becomehigh enough to deform the blade support discs. To these mechanicalstresses are added others particularly brought about by thermalexpansion of the compressor elements.

It has subsequently been proposed to replace the rotary diffuser with afixed diffuser with two walls prolonging the rotating blade supportdiscs and whose radii are limited in this case to those of the blades.The supersonic movement of the-fluid over the fixed walls, particularlythe downstream wall on which the pressure is generally higher because ofthe curved path followed by the fluid, leads to losses in efficiencysignificantly reducing the available increase in pressure ratio.

It has also been proposed to mount a diffuser arrangedto receive thefluid at supersonic speeds and having a convergent orconvergentdivergent profile downstream of the rotor.

These various proposals have not, however, provided a significantincrease, in the available compression ratio in a single compressorstage, and certain of them bring about output instabilities ormechanical difficulties.

SUMMARY OF THE INVENTION The invention is intended to provide animrpoved supersonic centrifugal compressor. 7

In accordance with the invention, a supersonic centrifugal compressorhas a rotor with substantially radially extending blades mounted on theface of a profiled support disc, the external diameter of the discexceeding that of the blades to form a disc extension. A fixed portionof the rotor casing has an internal surface so arranged that an annulardeceleration space is formed between that surface and the discextension, this deceleration space leading into a diffuser with fixedvanes defining passages inclined to the radial direction.

Using the invention, it is possible to reduce the disadvantages of thepreviously proposed compressors and to provide a high compression ratiowith a high and stable output.

The invention exploits the discovery that in providing a higherdeceleration than that obtained with an equiv alent rotary diffuser in aspace situated beyond the periphery of the rotor, it is possible notonly.to eliminate the mechanical difficulties of providing a rotor withtwo mobile blade support discs, but also to combine the compressor witha supersonic diffuser at whose entry the fluid is moving at a speed onlyslightly supersonic such that a system of weak shock waves is obtained.Thus, in the difi'user, the efficiency of the transformation of kineticenergy into pressure is increased, thereby increasing the overallefficiency.

According to the invention, this deceleration is ob tained between thefixed wall of the disc casing and the extension of the blade supportdisc.

The rotor casing is suitably adapted to define a fluid inlet, a rotorshroud confonning to the blade profile, said fixed portion of the rotorcasing, and opposite walls of the diffuser supporting fixed vanesthereof.

The diffuser preferably provides divergent passages generatingsubstantially plane re-compression waves.

The leading edges of the fixed vanes of the diffuser are suitably thinto be better adapted to supersonic operation.

The faces between which is defined the annular deceleration space,namely that of the fixed portion of the rotor casing and that of theblade disc extension, are preferably substantially parallel and providea significant deceleration of the supersonic flow between their insideand outside diameters.

It should be noted that this deceleration, as opposed to the case withpreviously proposed techniques, is obtained with friction losses reducedto a minimum and with lowered mechanical stresses. Because of the formof the passage within which the fluid is accelerated by the rotor, thefluid in the rotary diffuser exerts a higher pressure on the movingblade support disc which is moving at a relatively slow speed than onthe upstream wall which is fixed and with respect to which the fluid ismoving at high speed. It appears that this property of the compressorsignificantly increases the output and is an important contribution tothe very high pressure ratios obtained.

Moreover, it is known that the upstreamwall when rotating at high speedsundergoes important deformations because of its shape.

In the compressor provided by the invention, this wall is fixed and onlyexperiences thermal stresses which are easily mastered by one skilled inthe art.

The diffuser thus receives a flow which is sufficiently decelerated thatits speed is only slightly supersonic and it then becomes possible toset up a system of weak shockwaves and to obgain in the fixed diffuserand efficiency approaching unity.

The combination of the compressor rotor and diffuser is such that theincrease, in output obtained compensates the friction losses in thespace between the moving blades of the rotor and the fixed blades of thediffuser. The stability of the flow is increased and the rotor comprisesonly a single disc of increased radius so that better mechanicalstrength is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described inmore detail, by way of example only, with reference to the accompanyingdiagrammatic drawing, in which:

FIG. 1 is an axial section through the single stage supersoniccentrifugal compressor of the present invention, showing only that partof the compressor above its rotor axis.

FIG. 2 is a section through the compressor of FIG. 1 takenperpendicularly to its axis of rotation.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the present example, thecompressor serves for compressing air and has a compression ratio of theorder of 9.

Referring to the Figures, the compressor has a single rotor 1 withradially extending blades 2 mounted on the face of a profiled supportdisc 3. The external diameter of the disc 3 exceeds that of the blades 2to form a disc extension 3'.

The rotor shroud 5 is shaped to define a fluid inlet 11 and a rotorshroud 5" conforming to the profile of the blades 2. The internalsurface 5 of this rotor shroud 5" lies very close to the forward facesof the blades 2, as is clearly seen in FIG. 1. This profile is that of acone with curved generatrix.

The rotor casing continues to define a fixed wall portion facing thedisc extension 3', an annular deceleration space 4 being defined betweenthis fixed wall and the forward face of the extension 3' which, in useof the compressor, moves at a speed approaching that of the air undercompression. This deceleration space 4 leads into a diffuser 6 withfixed blades 9 supported between parallel annular walls formed bysections of the rotor casing.

As is seen clearly in FIG. 2, th diffuser 6 has six diverging passages 7defined by the fixed vanes 9 and arranged at an angle to the radialdirection. At the diffuser entry, the air under compression istravelling at supersonic speed.

The distance between the rim of the profiled support disc 3 and theleading edges 9' of the fixed blades 9 of the diffuser 6 is made verysmall, and is chosen to take into account the radial expansion of thedisc when turning at supersonic speed.

The rotor is keyed to a shaft shown schematically by its axis 10.

The internal face 5 of the rotor shroud 5 is made as small aspracticable so as to avoid loss of speed by the air. Where this faceextends beyond the blades 2, to define the disc extension 3' the annulardeceleration space 4, it runs substantially parallel to the front faceof the extension 3.

Where a particularly high output is required, any suitable form of flowdistributor may be mounted upstream of the rotor so as to reduce therelative speed of the air at the fluid entry 11. When the rotor isturning at 33,000 rpm, the rotary speed of the blade peripherycorresponds to a Mach number in the region of 1.3. The airspeed at theoutlet from the blades 2 is then of the order of Mach 1.2.

In the deceleration space 4 the airspeed decreases to a value less thanMach 1.1 by the time it reaches the leading edge 9' of the fixed vanes 9of the diffuser 6. The entry losses are negligible.

The air enters the diffuser 6 at a speed which is only slightlysupersonic and accelerates gradually to provide a recompression wave,when it decelerates inside the diffuser because of its now subsonicspeed.

The overall efficiency of a compressor stage such as just described mayreach some per cent.

It will be appreciated that a number of compressor stages such as justdescribed may be combined to provide a multi-stage compressor.

In the compressor just described, because of themcurving form of theinternal surface 5 of the rotor shroud, the air exerts on the extension3' a greater pressure than on the fixed wall of the rotor casing. Itappears that this property of the compressor provides a significantincrease in the output and has an important effect on the provision of ahigh compression ratio.

In the previously proposed rotary diffusers, the upstream diffuser wallsuffers significant deformations because of its form, in the compressorjust described this wall is fixed and so is subject only to thermaldeformations which are more readily compensated.

In the compressor just described, the diffuser receives a fluid flowwhich is sufficiently decelerated that its speed is only slightlysupersonic so that it is possible to obtain a system of weak shockwavesand consequently a diffuser efficiency approaching unity. Using theinvention, the increased efficiency obtained largely compensates thefriction losses encountered in the space between the moving blades ofthe rotor and the fixed blades of the diffuser. The stability of flow isimproved Moreover, since the rotor features only a single profiledsupport disc, it presents a better mechanical resistance.

We claim:

1. A supersonic centrifugal compressor comprising:

a rotor casing,

a rotor mounted for rotation about its axis within said casing,

said casing and said rotor having spaced opposed, similarly curvedsurfaces defining therebetween a gas flow path which changes from axialto radial,

a plurality of circumferentially spaced blades carried by said rotor andextending outwardly of said rotor surface from the vicinity of thecompressor axis throughout that portion of the flow path which changesfrom axial to radial,

said rotor surface being formed at its radially outboard end by a singleradial disc whose periphery extends radially beyond the outboard edgesof said blades to form a disc extension,

said rotor casing surface extending in a radial direction substantiallyparallel to said disc extension to form a gas deceleration chamber withsaid disc extension,

a diffuser chamber having fixed vanes defining passages leading fromsaid deceleration chamber and inclined to the radial direction, and

said fixed vanes of said diffuser chamber extending outwardly from apoint on said casing generally adjacent the periphery of said discextension.

2. The compressor as claimed in claim 1, wherein said casing includesaxially spaced fixed walls to define said diffuser chamber and tosupport said fixed diffuser vanes therebetween.

3. The compressor as claimed in claim 1, wherein the diffuser passagesare divergent.

4. The compressor as claimed in claim 2, wherein the diffuser passagesare divergent.

5. The compressor as claimed in claim 1, wherein the leading edges ofthe diffuser vanes have sharp edges for supersonic operation with lowlosses.

supersonic operation with los losses.

8. The compressor as claimed in claim 4, wherein the leading edges ofthe diffuser vanes have sharp edges for supersonic operation with lowlosses.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT N0. 3,771,925

DATED I NOV. 13, 1973 |NVENTOR(5) 1 Jean-Marie Eugene Friberg et al Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

On th COVeI sheet in item [301 Foreign Application Priority Data Jan.14, 1970, delete [Japan] and insert France and change the number of thepriority document to read 70 01 293 Signed and Scaled this eighth Day ofJunel976 [SEAL] Arrest:

RUTH C. MASON CJIARSHALL DANN Arresting Officer Commissioner ufPalemsand Trademarks

1. A supersonic centrifugal compressor comprising: a rotor casing, arotor mounted for rotation about its axis within said casing, saidcasing and said rotor having spaced opposed, similarly curved surfacesdefining therebetween a gas flow path which changes from axial toradial, a plurality of circumferentially spaced blades carried by saidrotor and extending outwardly of said rotor surface from the vicinity ofthe compressor axis throughout that portion of the flow path whichchanges from axial to radial, said rotor surface being formed at itsradially outboard end by a single radial disc whose periphery extendsradially beyond the outboard edges of said blades to form a discextension, said rotor casing surface extending in a radial directionsubstantially parallel to said disc extension to form a gas decelerationchamber with said disc extension, a diffuser chamber having fixed vanesdefining passages leading from said deceleration chamber and inclined tothe radial direction, and said fixed vanes of said diffuser chamberextending outwardly from a point on said casing generally adjacent theperiphery of said disc extension.
 2. The compressor as claimed in claim1, wherein said casing includes axially spaced fixed walls to definesaid diffuser chamber and to support said fixed diffuser vanestherebetween.
 3. The compressor as claimed in claim 1, wherein thediffuser passages are divergent.
 4. The compressor as claimed in claim2, wherein the diffuser passages are divergent.
 5. The compressor asclaimed in claim 1, wherein the leading edges of the diffuser vanes havesharp edges for supersonic operation with low losses.
 6. The compressoras claimed in claim 2, wherein the leading edges of the diffuser vaneshave sharp edges for supersonic operation with low losses.
 7. Thecompressor as claimed in claim 3, wherein the leading edges of thediffuser vanes have sharp edges for supersonic operation with loslosses.
 8. The compressor as claimed in claim 4, wherein the leadingedges of the diffuser vanes have sharp edges for supersonic operationwith low losses.